Assisting hand function after spinal cord injury with a fabric-based soft robotic glove.

BACKGROUND: Spinal cord injury is a devastating condition that can dramatically impact hand motor function. Passive and active assistive devices are becoming more commonly used to enhance lost hand strength and dexterity. Soft robotics is an emerging discipline that combines the classical principles of robotics with soft materials and could provide a new class of active assistive devices. Soft robotic assistive devices enable a human-robot interaction facilitated by compliant and light-weight structures. The scope of this work was to demonstrate that a fabric-based soft robotic glove can effectively assist participants affected by spinal cord injury in manipulating objects encountered in daily living. METHODS: The Toronto Rehabilitation Institute Hand Function Test was administered to 9 participants with C4-C7 spinal cord injuries to assess the functionality of the soft robotic glove. The test included object manipulation tasks commonly encountered during activities of daily living (ADL) and lift force measurements. The test was administered to each participant twice; once without the assistive glove to provide baseline data and once while wearing the assistive glove. The object manipulation subtests were evaluated using a linear mixed model, including interaction effects of variables such as time since injury. The lift force measures were separately evaluated using the Wilcoxon signed-rank test. RESULTS: The soft robotic glove improved object manipulation in ADL tasks. The difference in mean scores between baseline and assisted conditions was significant across all participants and for all manipulated objects. An improvement of 33.42 ± 15.43% relative to the maximal test score indicates that the glove sufficiently enhances hand function during ADL tasks. Moreover, lift force also increased when using the assistive soft robotic glove, further demonstrating the effectiveness of the device in assisting hand function. CONCLUSIONS: The results gathered in this study validate our fabric-based soft robotic glove as an effective device to assist hand function in individuals who have suffered upper limb paralysis following a spinal cord injury.

Amplifying and Leveraging Generated Force Upon Heating and Cooling in SMA Knitted Actuators.

This work reexamines traditional shape memory alloy (SMA) loading paths commonly used in SMA-based actuator applications and presents a novel, superimposed condition in which SMA generates substantial forces upon heating and cooling. This atypical effect, which is investigated with a textile-based actuator, was found to be prominent at the completion of material phase transformation, at which point thermal expansion/contraction became the dominant force-generating mechanism. We demonstrate that amplification of generated forces can be accomplished by varying the applied thermal load, applied structural strain, as well as actuator architecture. Specifically, we present SMA knitted actuators as an actuator architecture that increases the effect by aggregating SMA wires within a complex strain profile-effectively providing a larger operational window for the effect to propagate. The amplification of blocking forces through this novel operational procedure suggests reconsidering traditional blocking force design paradigms and opens untapped actuator application spaces, such as the highlighted medical and aerospace wearable technologies.

Dynamic Countermeasure Fabrics for Post-Spaceflight Orthostatic Intolerance.

INTRODUCTION: Aerospace orthostatic intolerance garments (OIG) have historically been pneumatic (e.g., NASA's antigravity suit), an approach that inhibits mobility and requires connection to an air supply. Elastic compression garments, an alternative technology, are difficult to don/doff and cannot be worn in a noncompressive state, resulting in discomfort and usability challenges. This research evaluates a novel technology-contractile shape memory alloy (SMA) knitted actuators-that can enable low-profile, dynamic compression for an aerospace OIG.METHODS: To characterize the functional capabilities of SMA knitted actuators, displacement control testing was conducted on 10 actuator samples with a range of geometric design parameters. Inactive (FI) and actuated forces (FA) were observed by repeatedly thermally cycling each sample at 0%, 15%, 30%, and 45% structural strain. Compression capabilities were approximated using medical compression hosiery standards and anthropometric data from a representative aerospace population (ANSUR 2012).RESULTS: Dynamic compression predictions reached 52 mmHg (single layer fabric) and 105 mmHg (double layer fabric) at the ankle. Low, inactive pressures (p < 20 mmHg) demonstrate that compression is controllable and can be dynamically increased upon actuation up to 33 mmHg in a single layer system and up to 67 mmHg in a double layer system.DISCUSSION: The results highlight the potential of SMA knitted actuators to enable low-profile, dynamic compression garments that can reach medically therapeutic pressures on an aerospace population to counteract OI symptoms. In addition to astronautic applications, this technology demonstrates widespread terrestrial medical and high-performance aircraft applicability.Granberry RM, Eschen KP, Ross AJ, Abel JM, Holschuh BT. Dynamic countermeasure fabrics for post-spaceflight orthostatic intolerance. Aerosp Med Hum Perform. 2020; 91(6):525-531.

EXPERIMENTAL INVESTIGATION OF THE MECHANISMS AND PERFORMANCE OF ACTIVE AUXETIC AND SHEARING TEXTILES.

Anisotropic textiles are commonly used in wearable applications to achieve varied bi-axial stress-strain behavior around the body. Auxetic textiles, specifically those that exhibit a negative Poisson's ratio (v), likewise exhibit intriguing behavior such as volume increase in response to impact or variable air permeability. Active textiles are traditional textile structures that integrate smart materials, such as shape memory alloys, shape memory polymers, or carbon nanotubes, to enable spatial actuation behavior, such as contraction for on-body compression or corrugation for haptic feedback. This research is a first experimental investigation into active auxetic and shearing textile structures. These textile structures leverage the bending- and torsional-deformations of the fibers/filaments within traditional textile structures as well as the shape memory effect of shape memory alloys to achieve novel, spatial performance. Five textile structures were fabricated from shape memory alloy wire deformed into needle lace and weft knit textile structures. All active structures exhibited anisotropic behavior and four of the five structures exhibited auxetic behavior upon free recovery, contracting in both x- and y-axes upon actuation (v = -0.3 to -1.5). One structure exhibited novel shearing behavior, with a mean free angle recovery of 7°. Temperature-controlled biaxial tensile testing was conducted to experimentally investigate actuation behavior and anisotropy of the designed structures. The presented design and performance of these active auxetic, anisotropic, and shearing textiles inspire new capabilities for applications, such as smart wearables, soft robotics, reconfigurable aerospace structures, and medical devices.

Functionally Graded Knitted Actuators with NiTi-Based Shape Memory Alloys for Topographically Self-Fitting Wearables.

Advances in actuating fabrics can enable a paradigm shift in the field of smart wearables by dynamically fitting themselves to the unique topography of the human body. Applications including soft wearable robotics, continuous health monitoring, and body-mounted haptic feedback systems are dependent upon simultaneous body proximity and garment stiffness for functionality. Passive fabrics and fitting mechanisms are unable to conform around surface concavities and require either high elasticity or a multiplicity of closure devices to achieve garment fit. The design, manufacture, and validation of the first circumferentially contractile and topographic self-fitting garments composed of NiTi-based shape memory alloy (SMA) knitted actuators that dynamically conform to the unique shape and size of the wearer's body in response to a change of the garment's temperature is introduced. Advanced materials and systems innovations 1) enable novel garment manufacturing and application strategies, 2) facilitate topographical fitting (spatial actuation) through garment architectural design, and 3) provide tunable NiTi-based SMA actuation temperatures to enable actuation on the surface of human skin. This research represents a paradigm shift for wearable applications by redefining garment fit to fully topographical conformation to the wearer through advanced materials and structures design.

Design and Control of Reduced Power Actuation for Active-Contracting Orthostatic Intolerance Garments.

Active-contracting fabrics are an emerging innovation that could revolutionize aerospace compression garment technology, notably orthostatic intolerance garments (OIG), by contracting on demand. Prior research has found that active-contracting fabrics, specifically weft knit garter fabric architectures constructed with shape memory alloy (SMA) filaments, can apply 2-54 mmHg on the body (single-layer construction) or 4-104 mmHg (double layer construction), depending on body radius. Prior garment prototyping and performance validation efforts have been conducted with commercially available Flexinol® wire with an actuation finish temperature of 90°C, a temperature that is not appropriate proximal to the human body. While other chemistries of SMA having lower actuation temperatures used for medical devices inside the human body (Tcore ≈ 37°C) are commonly available, SMA has not been optimized for actuation control against the human skin (TS ≈ 31°C). This research characterizes and validates a novel SMA material designed by Fort Wayne Metals specifically for actuation adjacent to the surface of the body. Through experimental temperature-force-displacement testing on both Dynalloy Flexinol® and Fort Wayne Metals straight SMA wire and SMA knitted actuator configurations, we present data that suggests (1) performance differences between low-temperature, nickel-rich SMA (Fort Wayne Metals) and high-temperature, titanium-rich SMA (Dynalloy Flexinol®) are negated by certain SMA knitted actuator structures, and (2) certain SMA knitted actuator configurations increase in force upon cool down, offering new concepts for SMA system actuation/control that minimize power consumption and waste heat. This manuscript presents experimental evidence for a future OIG that is donned in an oversized and compliant state, heated momentarily above ambient skin temperature to initiate actuation, and remain fully 'activated' once the actuation is complete upon equilibration with skin temperature. The result is an OIG that requires low-operating power that could be doffed through zipper releases and placed in a sub-zero chamber to return the structure to the 'off' state for reuse.

ACTIVE-CONTRACTING VARIABLE-STIFFNESS FABRICS FOR SELF-FITTING WEARABLES.

Self-fitting is the ability of a wearable, garment or body-mounted object to recover the exact shape and size of the human body. Self-fitting is highly desirable for wearable applications, ranging from medical and recreational health monitoring to wearable robotics and haptic feedback, because it enables complex devices to achieve accurate body proximity, which is often required for functionality. While garments designed with compliant fabrics can easily accomplish accurate fit for a range of body shapes and sizes, integrated actuators and sensors require fabric stiffness to prevent drift and deflection from the body surface. This paper merges smart materials and structures research with anthropometric analysis and functional apparel methodologies to present a novel, functionally gradient self-fitting garment designed to address the challenge of achieving accurate individual and population fit. This fully functional garment, constructed with contractile SMA knitted actuator fabrics, exhibits tunable %-actuation contractions between 4-50%, exerts minimal on-body pressure (≤1333 Pa or 10 mmHg), and can be designed to actuate fully self-powered with body heat. The primary challenge in the development of the proposed garment is to design a functionally gradient system that does not exert significant pressure on part of the leg and/or remain oversized in others. Our research presents a new methodology for the design of contractile SMA knitted actuator garments, describes the manufacture of such self-fitting garments, and concludes with an experimental analysis of the garment performance evaluated through three-dimensional marker tracking.

Exploiting Textile Mechanical Anisotropy for Fabric-Based Pneumatic Actuators.

Knit, woven, and nonwoven fabrics offer a diverse range of stretch and strain limiting mechanical properties that can be leveraged to produce tailored, whole-body deformation mechanics of soft robotic systems. This work presents new insights and methods for combining heterogeneous fabric material layers to create soft fabric-based actuators. This work demonstrates that a range of multi-degree-of-freedom motions can be generated by varying fabrics and their layered arrangements when a thin airtight bladder is inserted between them and inflated. Specifically, we present bending and straightening fabric-based actuators that are simple to manufacture, lightweight, require low operating pressures, display a high torque-to-weight ratio, and occupy a low volume in their unpressurized state. Their utility is demonstrated through their integration into a glove that actively assists hand opening and closing.